Over the past two decades, immunoassay or immunocytochemical assay methods have been developed which are useful in determining whether a particular analyte is present in a patient sample. In a typical immunoassay, an assay reagent is labeled with a compound that is capable of producing a detectable signal and that reagent is combined with a patient sample suspected of containing a particular analyte. The labeled assay reagent will bind to the analyte in an amount related to the amount of analyte in the sample.
Endogenous anti-analyte antibodies and immune complexes of antibodies and analyte circulating in serum samples have been found to interfere with analyte detection immunoassays. U.S. Pat. No. 4,703,001, describes a pretreatment method for disassociating immune complexes and denaturing anti-analyte antibodies for immunoassays for acid stable analytes in a serum sample comprising contacting the serum sample a pH dependent chaotrope at an acid pH. Similarly, P. Nishanian, et al. in J. Infect. Dis. 162:21-28 (1990), describe an acid hydrolysis serum sample pretreatment method that was used to disassociate analyte-anti-HIV antibodies immune complexes and denature anti-HIV antibodies. In order to obtain complete denaturation of the anti-HIV antibodies, however, the test serum was treated at 37.degree. C. for 60 minutes with a 0.5N HCl solution.
While acid hydrolysis, as performed for protein or peptide antigens, as described above, may provide accurate results, it is always desirable to achieve those results faster and with increased sensitivity. Moreover, such rigorous acid hydrolysis would not be permissible with some analytes. For example, the 2-keto-3-deoxyoctulosonic acid (KDO) sugars of lipopolysaccharide (LPS) antigens from certain microorganisms would be hydrolyzed by such treatment, thus destroying their antigenic activity. It would, therefore, be desirable to have an immunoassay method in which endogenous antibodies present in a patient sample can be irreversibly denatured at a pH greater than 7.0 and desirably at an alkaline pH without effecting the antigenicity of the analyte.